/
StackLimitEvader.cpp
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/
StackLimitEvader.cpp
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/*
This file is part of solidity.
solidity is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
solidity is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with solidity. If not, see <http://www.gnu.org/licenses/>.
*/
#include <libyul/optimiser/StackLimitEvader.h>
#include <libyul/optimiser/CallGraphGenerator.h>
#include <libyul/optimiser/FunctionCallFinder.h>
#include <libyul/optimiser/NameDispenser.h>
#include <libyul/optimiser/NameCollector.h>
#include <libyul/optimiser/StackToMemoryMover.h>
#include <libyul/backends/evm/ControlFlowGraphBuilder.h>
#include <libyul/backends/evm/EVMDialect.h>
#include <libyul/AsmAnalysis.h>
#include <libyul/AST.h>
#include <libyul/CompilabilityChecker.h>
#include <libyul/Exceptions.h>
#include <libyul/Object.h>
#include <libyul/Utilities.h>
#include <libsolutil/Algorithms.h>
#include <libsolutil/CommonData.h>
#include <range/v3/range/conversion.hpp>
#include <range/v3/view/concat.hpp>
#include <range/v3/view/take.hpp>
using namespace std;
using namespace solidity;
using namespace solidity::yul;
namespace
{
/**
* Walks the call graph using a Depth-First-Search assigning memory slots to variables.
* - The leaves of the call graph will get the lowest slot, increasing towards the root.
* - ``slotsRequiredForFunction`` maps a function to the number of slots it requires (which is also the
* next available slot that can be used by another function that calls this function).
* - For each function starting from the root of the call graph:
* - Visit all children that are not already visited.
* - Determine the maximum value ``n`` of the values of ``slotsRequiredForFunction`` among the children.
* - If the function itself contains variables that need memory slots, but is contained in a cycle,
* abort the process as failure.
* - If not, assign each variable its slot starting from ``n`` (incrementing it).
* - Assign ``n`` to ``slotsRequiredForFunction`` of the function.
*/
struct MemoryOffsetAllocator
{
uint64_t run(YulString _function = YulString{})
{
if (slotsRequiredForFunction.count(_function))
return slotsRequiredForFunction[_function];
// Assign to zero early to guard against recursive calls.
slotsRequiredForFunction[_function] = 0;
uint64_t requiredSlots = 0;
if (callGraph.count(_function))
for (YulString child: callGraph.at(_function))
requiredSlots = std::max(run(child), requiredSlots);
if (auto const* unreachables = util::valueOrNullptr(unreachableVariables, _function))
{
if (FunctionDefinition const* functionDefinition = util::valueOrDefault(functionDefinitions, _function, nullptr, util::allow_copy))
if (
size_t totalArgCount = functionDefinition->returnVariables.size() + functionDefinition->parameters.size();
totalArgCount > 16
)
for (TypedName const& var: ranges::concat_view(
functionDefinition->parameters,
functionDefinition->returnVariables
) | ranges::views::take(totalArgCount - 16))
slotAllocations[var.name] = requiredSlots++;
// Assign slots for all variables that become unreachable in the function body, if the above did not
// assign a slot for them already.
for (YulString variable: *unreachables)
// The empty case is a function with too many arguments or return values,
// which was already handled above.
if (!variable.empty() && !slotAllocations.count(variable))
slotAllocations[variable] = requiredSlots++;
}
return slotsRequiredForFunction[_function] = requiredSlots;
}
/// Maps function names to the set of unreachable variables in that function.
/// An empty variable name means that the function has too many arguments or return variables.
map<YulString, set<YulString>> const& unreachableVariables;
/// The graph of immediate function calls of all functions.
map<YulString, set<YulString>> const& callGraph;
/// Maps the name of each user-defined function to its definition.
map<YulString, FunctionDefinition const*> const& functionDefinitions;
/// Maps variable names to the memory slot the respective variable is assigned.
map<YulString, uint64_t> slotAllocations{};
/// Maps function names to the number of memory slots the respective function requires.
map<YulString, uint64_t> slotsRequiredForFunction{};
};
u256 literalArgumentValue(FunctionCall const& _call)
{
yulAssert(_call.arguments.size() == 1, "");
Literal const* literal = std::get_if<Literal>(&_call.arguments.front());
yulAssert(literal && literal->kind == LiteralKind::Number, "");
return valueOfLiteral(*literal);
}
}
void StackLimitEvader::run(
OptimiserStepContext& _context,
Object& _object
)
{
auto const* evmDialect = dynamic_cast<EVMDialect const*>(&_context.dialect);
yulAssert(
evmDialect && evmDialect->providesObjectAccess(),
"StackLimitEvader can only be run on objects using the EVMDialect with object access."
);
if (evmDialect && evmDialect->evmVersion().canOverchargeGasForCall())
{
yul::AsmAnalysisInfo analysisInfo = yul::AsmAnalyzer::analyzeStrictAssertCorrect(*evmDialect, _object);
unique_ptr<CFG> cfg = ControlFlowGraphBuilder::build(analysisInfo, *evmDialect, *_object.code);
run(_context, _object, StackLayoutGenerator::reportStackTooDeep(*cfg));
}
else
run(_context, _object, CompilabilityChecker{
_context.dialect,
_object,
true
}.unreachableVariables);
}
void StackLimitEvader::run(
OptimiserStepContext& _context,
Object& _object,
map<YulString, vector<StackLayoutGenerator::StackTooDeep>> const& _stackTooDeepErrors
)
{
map<YulString, set<YulString>> unreachableVariables;
for (auto&& [function, stackTooDeepErrors]: _stackTooDeepErrors)
// TODO: choose wisely.
for (auto const& stackTooDeepError: stackTooDeepErrors)
unreachableVariables[function] += stackTooDeepError.variableChoices | ranges::views::take(stackTooDeepError.deficit) | ranges::to<set<YulString>>;
run(_context, _object, unreachableVariables);
}
void StackLimitEvader::run(
OptimiserStepContext& _context,
Object& _object,
map<YulString, set<YulString>> const& _unreachableVariables
)
{
yulAssert(_object.code, "");
auto const* evmDialect = dynamic_cast<EVMDialect const*>(&_context.dialect);
yulAssert(
evmDialect && evmDialect->providesObjectAccess(),
"StackLimitEvader can only be run on objects using the EVMDialect with object access."
);
vector<FunctionCall*> memoryGuardCalls = FunctionCallFinder::run(
*_object.code,
"memoryguard"_yulstring
);
// Do not optimise, if no ``memoryguard`` call is found.
if (memoryGuardCalls.empty())
return;
// Make sure all calls to ``memoryguard`` we found have the same value as argument (otherwise, abort).
u256 reservedMemory = literalArgumentValue(*memoryGuardCalls.front());
yulAssert(reservedMemory < u256(1) << 32 - 1, "");
for (FunctionCall const* memoryGuardCall: memoryGuardCalls)
if (reservedMemory != literalArgumentValue(*memoryGuardCall))
return;
CallGraph callGraph = CallGraphGenerator::callGraph(*_object.code);
// We cannot move variables in recursive functions to fixed memory offsets.
for (YulString function: callGraph.recursiveFunctions())
if (_unreachableVariables.count(function))
return;
map<YulString, FunctionDefinition const*> functionDefinitions = allFunctionDefinitions(*_object.code);
MemoryOffsetAllocator memoryOffsetAllocator{_unreachableVariables, callGraph.functionCalls, functionDefinitions};
uint64_t requiredSlots = memoryOffsetAllocator.run();
yulAssert(requiredSlots < (uint64_t(1) << 32) - 1, "");
StackToMemoryMover::run(_context, reservedMemory, memoryOffsetAllocator.slotAllocations, requiredSlots, *_object.code);
reservedMemory += 32 * requiredSlots;
for (FunctionCall* memoryGuardCall: FunctionCallFinder::run(*_object.code, "memoryguard"_yulstring))
{
Literal* literal = std::get_if<Literal>(&memoryGuardCall->arguments.front());
yulAssert(literal && literal->kind == LiteralKind::Number, "");
literal->value = YulString{toCompactHexWithPrefix(reservedMemory)};
}
}